Acoustic device



C. KYLE ACOUSTIC DEVICE Filed March l2. 1928 Q QQ Q QQ bai) Sept. 30, 1930.

@QQ 0 9 G G@ @ooevooaoe @000000000 Patented Sept. 30, lg3d) lfllhll PATENT FFISE conm KYLE, or SAN Josn, CALIFORNIA,

ASSIGNOR, BY'MESNE ASSIGNMENTS, T0

UNITED BEPRODUCERS PATENTS CORPGRATION, F ST. CHARLES, ILLINOIS, A {30B- QPQJ'RATION 0F NEVADA.

ACOUSTIC DEVGE Application filed March 112, 1928. Serial No. 260,833.

This invention relates to a condenser, or electrostatic type 'of acoustic device, and especially to a modified form of the device shown in my former patent entitled Acoustic device Number 1,644,887 issued October 4 1927.

7The device show'n in the patent referred to consists of arigid perforated metallic plate, a thin flexible metallic plate and an l intermediate flexible dielectric diaphragm.

' the surface of the rigid plate.

An electric potential applied lto the plates causes electrostatic attraction which varies according to the degree of applied potential, and movement is therefore transmitted to the eXible metallic plate and the diaphragm, which produces sound or acoustic vibrations in the air coupled therewith.

I have discovered that the thickness of the dielectric diaphragm interposed between the rigid and the flexible plates, and the material employed in the diaphragm, plays an important factor in the successful operation of an acoustic device of the electrostatic type;

that is, materials such as thin sheets o mica,

Celluloid, treated pa er etc., presenting a hard, unyielding sur ace to the rigid `ertorated plate, and as such tend to pro uce a mechanical rattle or buzzing sound when the device is in operation. which are constructed of a sott or yielding material, such as thin sheets of rubber, rubberizcdsilk, linen, or cotton fabrics etc., are free from mechanical sounds, the hard or unyielding materials Such as paper, celluloid, mica etc., are.as a rule the best dielectrics and furthermore can be made much thinner. As such they are the most desirable, but the mechanical sound produced is so ob jectionable as to practically render such materials worthless.

l have now discovered that the mechanical' sound produced can be entirely avoided if a soft or yielding buffer material is interposed between the dielectric dia hragm and thin layer of this material is the equivalent of a soit pad interposed between two hard surfaces, and as such prevents rattle and buzzing sounds,

The object of the present invention is ac- While diaphrag'ms cordingly that ci generally improving and simplifying the construction and operation of acoustic devices of the character described, and particularly to interpose a soft buler material between the diaphragm and the rigid plate, so that diaphragm materials presenting a hard unyielding surface may be employed.

The invention is shown by way of illustration in the accompanying drawings, in which:

Fig. l is a plan view of the acoustic device, said plan view being partially in section and partially broken away to show the diierent plates, the diaphragm and the buffer material,

Fig. 2 is a transverse cross section of the acoustic device, i

Fig. 3 is an enlarged cross section of a portion of the acoustic device.

Referring to the drawings in detail, A indicates a rigid perforated metallic plate which is provided with an annular rim 2'. The plate may be constructed of practically any material, that is steel, iron, brass, copper, aluminum, etc., but it should be sufficiently thick or heavy to prevent it from. vibrating when the acoustic device is in operation. The plate may have any exterior contour desired but it is, in this instance, shown as circular or diskshaped in form. The surface presented is rounded or s herical, and it serves as a support for bu er material generally indicated at B, a flexible 'diaphragm C and .a flexible metallic plate generally 1ndicated at D. The buiier material is interposed between the rigid plate A and the diaphragm C, and a number of different buffer materials may be employed, such as a coatrolle'd into a thin leaf, such as goldleat, aluminum leaf, etc.,or it may consist of any electric conducting material, whether metallic or otherwise, such as graphite, sprayed metal, metal deposited by electrolytic action, plated, or a material dipped in asolution such as chloride lot gold etc.

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In one form ofthe invention as actually constructed -and used, an ordinary 'perforated steel plate of l-gauge metal is employed, as illustrated at A in the drawings; rlhis plate is cut circular or otherwise, and is providedwith a rim 2. The main face is hammered, or subjected to die action to produce a rounded or spherical surface. A. thin coating of rubber, as indicated at B, is then applied to one surface of the flexible diaphragm. rlhis coating of rubber may be partially vulcanized and the surface treated with soapstone or the' like, so as to reduce a resilient soft yield.

'ing'non-adhesive surface. The diaphragm is then stretched over the surface of the rigid plate A and is secured in any suitable manL ner, or as here shown by a clamping ring or band 3. The bul'er material contacts withthe upper surface of the plate A, and the diaphragm presenting a hard surface, may thus be employed, as mechanical rattle is prevented by the interposition ci the butler material.

After the diaphragm has been applied, a iexible metallic late may be formed, for instance by applying a thin coating of metal, by metallic spray, electrolytic deposition, plate, or by pasted gold leaf or the like, to the exterior surface of the diaphragm. 'lhe device so constructed is ready for use, and may be connected with any radio set whether transmitting or receiving, in fact may be ernployed in any circuit where transmission or 'reception ot sound is required, as it will function both as a microphone and as aloud speaker. It connected with a radio receiving set, it has power amplification in the audio frequency side otthe circuit. rli`lie two ter minals leading from the audio jfrequency amplifying circuit are connected, one to the eirible plate and one to the rigid plate. A'. modulated, or varying current potential is in this manner made with the surrounding atmosphere and the potentials imposed on maarre of a thin diaphragm is obvious, as the power or vlume output of the speaker is in direct ratio to the square of the distance between the two plates.' v

While certain features of the vpresent invention are more or less specifically described, l wish it understood that various changes may be resorted to withinl the scope of the a pended claims; similarly, that the materia s and finishes of the several-parts employed may be such as the manufacturer may decide or varying conditions or uses may demand.

1. An acoustic device comprising a rigid and a flexible plate, a diaphragm interposed between the plates, and a buier material inter osed between the diaphragm kand the rigid plate.

2. An acoustic device com rising a rigid and a flexible plate, atieXib e dielectric diaphragm interposed between the'plates, and a buffer material interposed between the diaphragm and the rigid plate. A

3. An acoustic device comprising a rigid and a flexible plate, a diaphragm interposed between the plates, and a dielectric bu'der material interposed between the diaphragm and the rigid plate.

t. An acoustic device comprising a rigid and a flexible plate, a diaphragm interposed between the plates, and a buer material secured to onev tace of the diaphragm and inf terposed between the diaphragm and the rigid plate.

5. An acoustic device comprising a rigid perforated plate, a dielectric diaphragm covering the plate, a soi-t yielding material secured to one face ot the diaphragm and interposed between the diaphragm and the rigid plate, and a tlenible electric conductor on the opposite tace ot the diaphragm.

the plates will be transmitted into sound or acoustic vibrations.,

l Jfound that an ideal buier between the diaphnagni and the rigid plate'inay be termed by applyingl a thin coatin ot rubber ceinented` to t e inner tace o. the diaphragm 'and then sprinkling on. a thin coating ot granulated rubber, such as shown at e (see Fig. 3l. This prevents Contact of the hard lsurfaces et the diaphragm and the rigid plate, and mechanical sound is completely eliminated. The louder material accordingly ermite use ot diaphragm materials heretoore considered im ractical, and it permits use of thinner diep regine, The importance 

